This invention relates generally to infusion systems for the administration of medications. More particularly, the present invention relates to a refillable and subcutaneously implantable medication delivery system including means for limiting the total amount of medication which can be infused therethrough over a given period of time.
The administration of medications over sustained periods of time is necessary in the treatment of several various medical conditions. For instance, it is often desirable to provide a pain killer, such as morphine, to terminally ill patients to help them cope with the sometimes excruciating pain which accompanies certain diseases. Terminally ill patients frequently experience such extreme pain that hospitalization becomes necessary to provide medications at intervals and in quantities sufficient to meet the patient's needs. Alternatively, when hospitalization is not acceptable the patient is often required to obtain private nursing care.
Requiring a terminally ill patient to either be hospitalized or to arrange for private nursing care can become a substantial burden upon both the health care system and the patient. Health care facilities are increasingly burdened as the demand for hospital bed space increases at a rate greater than the growth in available bed space. This burden is accentuated when patients, such as terminally ill patients, are hospitalized for want of an alternative treatment methodology. Also, the diversion of medically trained personnel to deal with the routine infusion of medications imposes additional burdens on the health care system which could be avoided provided the proper technology were available.
When patients must be confined to a hospital bed or arrange for private duty nursing care to receive prescribed medications, the costs involved often exceed the financial means of such patients. For example, many terminally ill patients cannot afford to pay for the expensive and individualized care which could make the last period of time prior to death much more productive and less difficult for the patient and for those around him. Indeed, some patients cannot afford any medical care whatsoever and their only available alternative is to forego treatment. Sometimes patients who cannot afford the hospitalization or private nursing care required and who cannot tolerate the pain involved with a particular disease must be hospitalized at society's expense.
These burdens to the patient, the health care system and to society in general have prompted several changes in health care methodology. For instance, many physicians have found it desirable to administer prescribed medications on an outpatient basis. This outpatient technique has proven to be effective in substantially reducing the costs associated in the treatment of many types of ailments; however, there have been a number of drawbacks which have made such outpatient arrangements less than ideal.
A typical drawback of outpatient treatment programs involves the requirement of frequent visits by the patient with the physician and the resultant time and transportation problems. If the patient could be provided adequate home care for extended periods of time, the time between visits with the physician would be lengthened. Such extended home care would benefit the physician as well as the patient in many circumstances, by permitting the physician to devote more professional time to other important matters.
Notwithstanding the foregoing, some patients find that receiving regular injections of medication over a prolonged period of time is distasteful, not to mention painful. It has been found that repeated injections through the skin into a specific, limited area of the body can be harmful to the patient and can sometimes cause problems which could become more threatening to the well-being of the patient than the illness being treated. Such problems have made necessary the use of alternate injection sites, the rotation of injections among alternate injection sites, or, in the extreme, the abandonment of medication injections as a useful form of treatment. Moreover, some substances have been found to traumatize the skin when injected, and this has necessitated the use of alternative means for introducing such substances into the body. Such alternate introduction means have included the use of catheters which are inserted through the skin into the body and have a portion which remains extended through the patient's skin to provide external access. This and similar methods and systems have proven to be undesirable for extended treatment because of the risk of infection at the incision site where the catheter extends through the skin.
In an effort to overcome the above-noted drawbacks associated with prior treatment procedures, several types of drug delivery devices have been developed which permit the self-administration of medication in precise quantities while minimizing the number of injections required and visits which need be made with a physician. Exemplary of such prior drug delivery devices are those illustrated in U.S. Pat. Nos. 4,588,394 and 4,681,560, the contents of which are incorporated herein by reference. These prior systems are constructed for total subcutaneous emplacement in the body, include appropriate devices to prevent the unintended infusion of the medication from the system into the body, and are refillable by injection to permit long term use. Such devices may be useful not only in the administration of medication to terminally ill patients, but also in the administration of other medications, such as insulin to diabetic patients.
The development of infusion systems which are totally subcutaneously emplaced in the body and which are actuated by manual percutaneous manipulation, has caused some medical professionals to worry that such devices may pose a danger to the patient since the medication is self-administered. In the case of a terminally ill patient, there is a danger that the patient or another giving care to the patient may infuse too great a quantity of a substance such as morphine through the system, in the absence of suitable safeguards. Similarly, in the case of diabetic patients, there is a danger, or at least the possibility, that too great a quantity of insulin could be self-administered through implantable and manually actuable systems and devices.
In efforts to ensure that medication is not accidentally infused into the patient, prior implantable infusion systems are usually designed to require at least two positive percutaneous manipulative steps before medication is permitted to pass into a delivery catheter for infusion into the body. The above-referenced patents show good examples of prior devices incorporating such safeguards. Some medical professionals have opted not to give the patient the opportunity to self-administer medication, but regulate the rate of medication infusion through systems powered by internal batteries or external power sources.
Accordingly, there has been a need in the medical arts for implantable infusion systems which allow the patient to administer required medications in precise quantities while minimizing the number of injections required and visits which need be made with a physician. Such infusion systems are needed which inherently limit the amount of medication which can be infused into the patient over a given period of time. Preferably, such limitation on the total amount of medication which can be infused over a given period of time can be accomplished independently of the size of a reservoir for storing the medication. Further, a novel medication delivery device is needed which may be totally subcutaneously emplaced in the body, includes appropriate devices to prevent the unintended infusion of the medication from the system to the body, is refillable by injection to permit long-term use, and includes an inherent recharge restriction capability for limiting the rate at which medication may be infused to the body while preserving the ability of the patient to self-administer the medication on demand in a safe and reliable manner. Moreover, such a medication delivery device should be constructed to facilitate autoclave sterilization thereof, without limiting the desired characteristics of the device. The present invention fulfills these needs and provides other related advantages.